Paracetamol Dosage Calculator

The bottle in your hand beats this page

Start here, because it matters more than anything else below. The dosing instructions on the pack you actually own are the instructions to follow. They are written for that specific product, at that specific strength, in your specific country, and they are what your pharmacist will point at if you ask.

What this calculator is for is checking. It runs the standard weight-based sum that sits behind those labels, which is genuinely useful when the label gives you a broad age band and your child is small or large for their age, or when you want to understand where the number on the bottle came from. It is a second opinion on arithmetic, not a first opinion on treatment.

Paracetamol is a good medicine with a narrow margin. The therapeutic dose and the harmful dose are closer together than most people assume, and it is the most common cause of acute liver injury from medicine in many countries. None of that means you should be frightened of it. It means the number is worth getting right, and the sections below are about the places it goes wrong.

Why it asks for weight and not just age

Because age is a poor proxy for size, and paracetamol is dosed by size.

Two four-year-olds can differ by 8 kg or more. Dose them both by their birthday and one gets too little, which means their fever is not treated and you dose again sooner than you should, and one gets too much. Manufacturers themselves say weight is the preferred basis and that age should only be used when weight is not available, and the clinical guidance follows the same rule.

So the tool asks for age only to decide whether to answer at all, and then does everything from weight. If you are working from a label that gives age bands, and your child sits at the edge of a band or well off the average for their age, weight-based arithmetic is the more accurate route. Bring it up with your pharmacist rather than acting on it alone.

The two numbers it gives you

Both come from the standard paediatric dosing used internationally:

Those two figures fit together deliberately. Four doses of 15 mg/kg comes to exactly 60 mg/kg, which is why the tool tells you a maximum of four doses in 24 hours. The daily ceiling is not a separate rule; it is the single dose multiplied by the number of times you are allowed to give it.

The caps matter for older children. Above roughly 67 kg the weight-based sum would exceed the adult dose, so it stops there. A teenager who weighs more than an adult does not get more than an adult.

A worked example

A child weighing 15 kg:

Single dose = 15 × 15 mg = 225 mg
Daily maximum = 15 × 60 mg = 900 mg
Given as: up to four doses of 225 mg, at least four hours apart

Sanity check the daily figure yourself: four lots of 225 is 900. If those two numbers ever fail to line up, something has gone wrong.

If your scales read in pounds, the tool converts for you. A child of 33 lbs is about 15 kg, and lands on the same 225 mg.

Milligrams are not millilitres, and this is where it goes wrong

This is the most important section on the page. The calculator gives you milligrams. Your bottle is measured in millilitres. Those are not the same thing, and the gap between them is where children get hurt.

Children's paracetamol comes in more than one strength. Two are common:

• 120 mg per 5 ml, the infant suspension, typically for roughly 3 months to 6 years.
• 250 mg per 5 ml, the stronger suspension, typically for 6 years and over.

Same medicine. Same-looking bottle. Twice the concentration. Take our 15 kg child needing 225 mg:

Read that twice. Measure out 9.4 ml from the 250 mg bottle because that is the number you remembered, and you have given roughly 470 mg, more than double the dose. Do that four times in a day and you are near 1,900 mg in a child whose daily ceiling is 900.

So, every time:

• Check the strength printed on the bottle, not the one you used last time or the one at your mother's house.
• Convert deliberately: millilitres = (dose in mg ÷ strength in mg) × 5. For 225 mg from a 120 mg/5 ml bottle: (225 ÷ 120) × 5 = 9.4 ml.
• Use the syringe or cup that came with that bottle. Kitchen spoons are not measuring instruments and vary enormously.
• If you have two bottles in the house, check which one you are holding. Every time, including at 3am, especially at 3am.

If any of that feels uncertain, a pharmacist will do the conversion with you in thirty seconds and will not mind being asked.

Why a baby under 3 months gets no number

Enter an age under three months and the tool refuses to produce a dose. That is deliberate, and it is not the calculator being unhelpful.

Very young infants clear paracetamol differently, they are dosed on a different basis, and they have the least room to absorb an error. Standard guidance is that paracetamol for a baby this young should be directed by a doctor or pharmacist rather than taken from any chart.

There is a second reason, and it is the more urgent one. A fever in a baby under three months is not a symptom to be medicated at home; it is a reason to be seen the same day. Young infants can be seriously unwell with very few outward signs, and bringing a temperature down with paracetamol can mask the very thing a clinician needs to see. If your baby under three months has a fever, please contact a doctor now rather than looking for a dose.

The four-hour gap and the four-dose ceiling

Two rules, and they apply together rather than separately:

• At least four hours between doses. Standard guidance is every four to six hours, so four is the floor and not the target.
• No more than four doses in 24 hours. This is a rolling 24 hours, not a calendar day, which is the bit people miss. A dose at 11pm counts against tomorrow.

Both rules exist because paracetamol accumulates. It is cleared by the liver at a fixed pace, and giving the next dose too early stacks it. The overdoses that come from a bottle at home are usually not one enormous dose; they are ordinary doses given a little too often, by tired people who lost track.

Which suggests the single most useful habit: write the times down. A scrap of paper by the bottle, or a note on your phone. Anyone else in the house who might give a dose then knows what has already gone in. That one piece of paper prevents most of the double-dosing there is.

The paracetamol hiding in other medicines

Paracetamol is not only sold as paracetamol. It is an ingredient in a great many combination products, and this is a leading route to accidental overdose because nobody thinks they have taken two doses of anything.

Watch for it in:

• Cold and flu remedies, especially the sachets you dissolve in hot water.
• Night-time or "all-in-one" cough and cold preparations.
• Combined painkillers, including anything pairing paracetamol with codeine or caffeine.
• Suppositories. These absolutely count towards the daily total, and forgetting them is a known cause of overdose.

It may be listed as acetaminophen rather than paracetamol, which is the same drug under its other name. So before giving a dose, read the ingredients of everything else your child has had. If a cold remedy already contains it, that dose is part of the day's total.

Ibuprofen is a different drug and does not count towards the paracetamol total. Some clinicians do advise alternating the two, but that is a decision to make with your doctor or pharmacist rather than on your own, because it doubles the number of things you are tracking at the exact moment you are least able to track them.

What an overdose looks like early, which is nothing

This is the fact that makes paracetamol dangerous in a way people do not expect, and it deserves to be stated plainly.

In the early hours after a paracetamol overdose, there are usually no useful symptoms. Perhaps some nausea. Often nothing at all. The person looks fine, and because they look fine, everyone waits. By the time there are obvious signs, which can be a couple of days later, serious liver damage may already have happened.

The treatment works, and it works best when it is given early. That combination, an antidote that works early and a poisoning that hides early, is the whole reason for the following rule:

If you think too much paracetamol has been taken, get medical help immediately. Do not wait to see whether symptoms appear. Do not wait until morning.

Contact your poisons centre, your doctor, or your local emergency number now, and take the packet with you so they can see the product and the strength. It does not matter whether it was a child who found a bottle, a miscalculation with a syringe, or doses given too close together across a long night. The right response is the same, and it is to ask someone straight away. Nobody will think you were foolish for checking. This is one of the most common reasons people contact poisons services anywhere in the world.

When paracetamol is not the answer

Worth a moment, because the reflex to treat every temperature is strong and not always right.

Fever is part of how a body fights infection, not the illness itself. The reason to give paracetamol is that your child is uncomfortable, not that a thermometer showed a number. A child with a temperature who is drinking, playing and reasonably content may not need medicating at all, and treating the number rather than the child is how people end up giving more than they need to.

Please speak to a doctor rather than reaching for another dose if:

• Your baby is under three months and has any fever.
• A fever lasts more than about three days, or keeps returning.
• Your child is drowsy and hard to rouse, floppy, or not responding normally.
• There is a rash that does not fade when pressed, a stiff neck, or laboured breathing.
• They are not drinking, or you are seeing dry nappies and no tears.
• Something is simply wrong in a way you cannot name. Parental instinct is decent evidence and clinicians take it seriously.

Those are all reasons a calculator cannot help with, which is the honest summary of this page: it does one small sum, and the sum is the easy part.

Questions people ask

How much paracetamol for a 15 kg child?

225 mg per dose, up to four doses in 24 hours, at least four hours apart, giving a daily maximum of 900 mg. In liquid, 225 mg is about 9.4 ml of a 120 mg/5 ml suspension or about 4.5 ml of a 250 mg/5 ml one. Check which strength your bottle is before measuring, and follow the pack.

The calculator gives mg but my bottle is in ml. How do I convert?

Millilitres = (dose in mg ÷ the bottle's mg figure) × 5. So 225 mg from a 120 mg/5 ml bottle is (225 ÷ 120) × 5 = 9.4 ml. The strength is printed on the label and is not the same across products, so do this conversion with the actual bottle in your hand, using the syringe that came with it.

I think I gave a dose twice. What should I do?

Contact a doctor, pharmacist or your poisons centre now, and do not wait to see whether your child seems unwell. Early paracetamol overdose often has no symptoms at all, and treatment works best when it is given early. Have the packet to hand so they can see the strength. Checking is always reasonable.

Can I give paracetamol to my 2-month-old?

Not on the basis of this tool, which is why it declines to give a number. A baby that young needs a dose directed by a doctor or pharmacist. And if the reason you are asking is a fever, please contact a doctor today: fever in a baby under three months always warrants being seen.

Can I give ibuprofen as well?

They are different drugs, so ibuprofen does not count towards the paracetamol total, and alternating them is something clinicians do recommend in some situations. But it is a conversation to have with your doctor or pharmacist first, partly because ibuprofen has its own rules, and partly because tracking two medicines at once is exactly when mistakes happen. If you do it, write down every dose of both.

The bottle's age chart says something different from this calculator. Which is right?

Follow the bottle. Age-band charts are deliberately built with a margin and are matched to that exact product. The weight-based sum here is more precise in principle, and it is useful for understanding the label or for a child well off the average for their age, but a disagreement is a reason to ask a pharmacist rather than to override the pack.

References

Where the figures come from. The dosing used by this tool, 15 mg/kg given three or four times daily to a maximum of 60 mg/kg per day for children, alongside the adult ceilings of 1 g per dose and 4 g per day, is the standard set out in the MSF essential medicines guidance. The four-to-six hour interval, the maximum of four doses in 24 hours, the common suspension strengths of 120 mg/5 ml and 250 mg/5 ml, and the age bands they correspond to follow the NHS oral paracetamol dosing guidance.

1. Paracetamol (acetaminophen), oral. MSF Medical Guidelines, Essential Drugs. medicalguidelines.msf.org
2. Guidance for Oral Paracetamol Dosing. NHS (Barnsley) BEST formulary guidance. best.barnsleyccg.nhs.uk